This invention relates to a radially expandable stent having a reduced profile in the unexpanded state.
Surgical stents have long been known which can be surgically implanted into a body lumen, such as an artery, to reinforce, support, repair or otherwise enhance the performance of the lumen. For instance, in cardiovascular surgery it is often desirable to place a stent in the coronary artery at a location where the artery is damaged or is susceptible to collapse. The stent, once in place, reinforces that portion of the artery allowing normal blood flow to occur through the artery. One form of stent which is particularly desirable for implantation in arteries and other body lumens is a cylindrical stent which can be radially expanded from a first smaller diameter to a second larger diameter. Such radially expandable stents can be inserted into the artery by being located on a catheter and fed internally through the arterial pathways of the patient until the unexpanded stent is located where desired. The catheter is fitted with a balloon or other expansion mechanism which exerts a radial pressure outward on the stent causing the stent to expand radially to a larger diameter. Still other stents are self-expanding. Regardless of the expansion method, expandable stents exhibit sufficient rigidity after being expanded that they will remain expanded after the catheter has been removed.
Radially expandable stents come in a variety of different configurations to provide optimal performance in various different particular circumstances. For instance, the patents to Lau (U.S. Pat. Nos. 5,514,154, 5,421,955, and 5,242,399), Baracci (U.S. Pat. No. 5,531,741), Gaterud (U.S. Pat. No. 5,522,882), Gianturco (U.S. Pat. Nos. 5,507,771 and 5,314,444), Termin (U.S. Pat. No. 5,496,277), Lane (U.S. Pat. No. 5,494,029), Maeda (U.S. Pat. No. 5,507,767), Marin (U.S. Pat. No. 5,443,477), Khosravi (U.S. Pat. No. 5,441,515), Jessen (U.S. Pat. No. 5,425,739), Hickle (U.S. Pat. No. 5,139,480), Schatz (U.S. Pat. No. 5,195,984), Fordenbacher (U.S. Pat. No. 5,549,662) and Wiktor (U.S. Pat. No. 5,133,732), each include some form of radially expandable stent for implantation into a body lumen.
As the above listed patents demonstrate, a wide variety of stents are known in the prior art. Typically, stents are tube-shaped. FIGS. 1-3 show an example of a prior art stent. As shown, the prior art stents often comprise a plurality of cylindrical, serpentine rings joined by connecting members. For deployment, stents are usually compressed to a low profile and crimped onto a catheter, and advanced through tortuous passageways in a patient's body to be deployed into a blood vessel or other body lumen where they are radially expanded.
FIG. 1 shows a prior art stent 10 mounted on a catheter device 14 in a pre-deployment configuration. Before insertion into a patient's body, the stent 10 is placed over the expandable balloon 18 and crimped onto the balloon in order to form a reduced profile for insertion into the body through small diameter, tortuous-pathed arteries or other vessels or lumens within the body. In other prior art systems, a self-expanding stent may be utilized. Typically, the catheter device 14 is advanced through a patient's body by deploying a small guide wire (not shown) and advancing the catheter device over the guide wire to its final destination such as a partially blocked artery 22. The balloon 18 is then inflated by methods known in the art to expand the stent radially so that the stent abuts against the walls of the artery as shown in FIG. 2. After deployment, the balloon is deflated, and the catheter device is removed from the patient's body. The stent 10 remains in the expanded configuration in the artery to hold the artery open and prevent further blockage.
However, prior art stents typically have problems with their ability to be crimped to a low profile for deployment into an artery or blood vessel. This makes it difficult to deliver the stent to its deployment location inside a small diameter, tortuous pathed artery. Additionally, the configurations of the prior art stents typically lead to problems with high stresses at various portions of the stent when crimped.
For example, FIG. 3 shows an enlarged view of the prior art stent 10 of FIG. 2 in an expanded configuration within an artery 22. The stent 10 utilizes a plurality of ring structures 24 interconnected by a plurality of generally straight connector members 26. In other prior art, the connector members 26 may have curved portions, such as U, V, or W shaped portions. Each ring structure 24 comprises an endless pattern of unit structures 30. The unit structures 30 are made up of a repeated pattern of a plurality of struts 34 joined together by bends or apexes 38. However, the configuration of the connector members 26 and bends 38 leads to increased stress in the stent 10 at the bends when the stent is in a crimped configuration prior to expansion within an artery. In an effort to alleviate this problem, some prior art stents have used stress-relieving bends (or apexes), which have bends extending outwardly from the struts in a key-hole shape or other outwardly extending shape, to reduce bending stresses. However, in many prior art stents utilizing stress-relieving bends, in the crimped, non-expanded configuration the bends 38 abut against each other thereby limiting how far the stent 10 may be crimped. As a result, it is more difficult to deliver these stents to their deployment location inside a vessel due to their enlarged profile.
What is needed is a stent which can be crimped to a reduced profile with reduced stress on the stent, while maintaining the strength and flexibility of the stent so that it can be advanced through the narrow passageways present in a patient's body and then expanded to dilate and/or circumferentially support the vessel wall. The present invention satisfies these and other needs.